feat: add Linear OAuth integration and connector routes

- Introduced Linear OAuth support with new environment variables for client ID, client secret, and redirect URI.
- Implemented Linear connector routes for OAuth flow, including authorization and callback handling.
- Updated existing components to accommodate Linear integration, including validation changes and connector configuration.
- Enhanced the Linear indexer to utilize OAuth access tokens instead of API keys.
- Adjusted UI components to reflect the new Linear connector without requiring special configuration.

surfsense_backend/app/utils/validators.py

@@ -532,7 +532,6 @@ def validate_connector_config(
                 )
             },
         },
-        "LINEAR_CONNECTOR": {"required": ["LINEAR_API_KEY"], "validators": {}},
         "DISCORD_CONNECTOR": {"required": ["DISCORD_BOT_TOKEN"], "validators": {}},
         "JIRA_CONNECTOR": {
             "required": ["JIRA_EMAIL", "JIRA_API_TOKEN", "JIRA_BASE_URL"],